// SPDX-License-Identifier: GPL-2.0-only /* * kernel/freezer.c - Function to freeze a process * * Originally from kernel/power/process.c */ #include <linux/interrupt.h> #include <linux/suspend.h> #include <linux/export.h> #include <linux/syscalls.h> #include <linux/freezer.h> #include <linux/kthread.h> /* total number of freezing conditions in effect */ DEFINE_STATIC_KEY_FALSE(freezer_active); EXPORT_SYMBOL(freezer_active); /* * indicate whether PM freezing is in effect, protected by * system_transition_mutex */ bool pm_freezing; bool pm_nosig_freezing; /* protects freezing and frozen transitions */ static DEFINE_SPINLOCK(freezer_lock); /** * freezing_slow_path - slow path for testing whether a task needs to be frozen * @p: task to be tested * * This function is called by freezing() if freezer_active isn't zero * and tests whether @p needs to enter and stay in frozen state. Can be * called under any context. The freezers are responsible for ensuring the * target tasks see the updated state. */ bool freezing_slow_path(struct task_struct *p) { if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK)) return false; if (test_tsk_thread_flag(p, TIF_MEMDIE)) return false; if (pm_nosig_freezing || cgroup_freezing(p)) return true; if (pm_freezing && !(p->flags & PF_KTHREAD)) return true; return false; } EXPORT_SYMBOL(freezing_slow_path); bool frozen(struct task_struct *p) { return READ_ONCE(p->__state) & TASK_FROZEN; } /* Refrigerator is place where frozen processes are stored :-). */ bool __refrigerator(bool check_kthr_stop) { unsigned int state = get_current_state(); bool was_frozen = false; pr_debug("%s entered refrigerator\n", current->comm); WARN_ON_ONCE(state && !(state & TASK_NORMAL)); for (;;) { bool freeze; raw_spin_lock_irq(¤t->pi_lock); set_current_state(TASK_FROZEN); /* unstale saved_state so that __thaw_task() will wake us up */ current->saved_state = TASK_RUNNING; raw_spin_unlock_irq(¤t->pi_lock); spin_lock_irq(&freezer_lock); freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop()); spin_unlock_irq(&freezer_lock); if (!freeze) break; was_frozen = true; schedule(); } __set_current_state(TASK_RUNNING); pr_debug("%s left refrigerator\n", current->comm); return was_frozen; } EXPORT_SYMBOL(__refrigerator); static void fake_signal_wake_up(struct task_struct *p) { unsigned long flags; if (lock_task_sighand(p, &flags)) { signal_wake_up(p, 0); unlock_task_sighand(p, &flags); } } static int __set_task_frozen(struct task_struct *p, void *arg) { unsigned int state = READ_ONCE(p->__state); if (p->on_rq) return 0; if (p != current && task_curr(p)) return 0; if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED))) return 0; /* * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they * can suffer spurious wakeups. */ if (state & TASK_FREEZABLE) WARN_ON_ONCE(!(state & TASK_NORMAL)); #ifdef CONFIG_LOCKDEP /* * It's dangerous to freeze with locks held; there be dragons there. */ if (!(state & __TASK_FREEZABLE_UNSAFE)) WARN_ON_ONCE(debug_locks && p->lockdep_depth); #endif p->saved_state = p->__state; WRITE_ONCE(p->__state, TASK_FROZEN); return TASK_FROZEN; } static bool __freeze_task(struct task_struct *p) { /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */ return task_call_func(p, __set_task_frozen, NULL); } /** * freeze_task - send a freeze request to given task * @p: task to send the request to * * If @p is freezing, the freeze request is sent either by sending a fake * signal (if it's not a kernel thread) or waking it up (if it's a kernel * thread). * * RETURNS: * %false, if @p is not freezing or already frozen; %true, otherwise */ bool freeze_task(struct task_struct *p) { unsigned long flags; spin_lock_irqsave(&freezer_lock, flags); if (!freezing(p) || frozen(p) || __freeze_task(p)) { spin_unlock_irqrestore(&freezer_lock, flags); return false; } if (!(p->flags & PF_KTHREAD)) fake_signal_wake_up(p); else wake_up_state(p, TASK_NORMAL); spin_unlock_irqrestore(&freezer_lock, flags); return true; } /* * Restore the saved_state before the task entered freezer. For typical task * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state * is restored unless they got an expected wakeup (see ttwu_state_match()). * Returns 1 if the task state was restored. */ static int __restore_freezer_state(struct task_struct *p, void *arg) { unsigned int state = p->saved_state; if (state != TASK_RUNNING) { WRITE_ONCE(p->__state, state); p->saved_state = TASK_RUNNING; return 1; } return 0; } void __thaw_task(struct task_struct *p) { unsigned long flags; spin_lock_irqsave(&freezer_lock, flags); if (WARN_ON_ONCE(freezing(p))) goto unlock; if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL)) goto unlock; wake_up_state(p, TASK_FROZEN); unlock: spin_unlock_irqrestore(&freezer_lock, flags); } /** * set_freezable - make %current freezable * * Mark %current freezable and enter refrigerator if necessary. */ bool set_freezable(void) { might_sleep(); /* * Modify flags while holding freezer_lock. This ensures the * freezer notices that we aren't frozen yet or the freezing * condition is visible to try_to_freeze() below. */ spin_lock_irq(&freezer_lock); current->flags &= ~PF_NOFREEZE; spin_unlock_irq(&freezer_lock); return try_to_freeze(); } EXPORT_SYMBOL(set_freezable);